In the manufacture of electronic devices such as semiconductor devices or the like, a metal film is formed on a substrate. The metal film is used as, for example, a wiring layer. A tungsten film is known as such a metal film.
Various methods of forming a tungsten film have been used. Tungsten films formed using such methods includes a first tungsten film and a second tungsten film. In these methods, a raw material gas containing tungsten and a reducing gas are alternately supplied to a substrate together with a carrier gas. As a result, the first tungsten film is formed. The raw material gas contains tungsten hexafluoride, and the reducing gas is a hydrogen-containing gas such as diborane or the like. Subsequently, a raw material gas containing tungsten and a reducing gas are alternately supplied to the substrate together with a carrier gas. As a result, a second tungsten film is formed on the first tungsten film. In the formation of the second tungsten film, the raw material gas contains tungsten hexafluoride, and the reducing gas is hydrogen gas. The carrier gas used in forming the first and second tungsten films is an inert gas such as a nitrogen gas or a noble gas.
As described above, the tungsten film is used as, for example, a wiring layer. Therefore, the tungsten film resistance needs to be low.